1. Field of the Invention
The present invention relates to a motor control apparatus and motor control method, and more specifically, it relates to an apparatus of and method for controlling a motor to reduce the higher harmonic current flowing to a 3-phase AC motor.
2. Description of the Related Art
The applicant of the present invention has proposed a motor control apparatus that reduces the higher harmonic current flowing to a 3-phase AC motor (Japanese Patent Application No. 2000-356117). This motor control apparatus includes a fundamental current control system that controls a fundamental current in a dq-axis orthogonal coordinate system rotating in synchronization with the rotation of the 3-phase AC motor and a higher harmonic current control system that controls a higher harmonic current in a dhqh-axis orthogonal coordinate system (a higher harmonic coordinate system) rotating at a frequency that is an integral multiple of the frequency of the fundamental component of the motor current.
In a steady state, the fundamental current is a direct current and the higher harmonic current is an alternating current in the dq-axis coordinate system in this motor control apparatus. Accordingly, the higher harmonic current manifesting as the alternating current quantity is extracted from the current in the dq-axis coordinate system by using a high pass filter and the extracted current is converted to a higher harmonic current in the dhqh-axis higher harmonic coordinate system so as to handle the higher harmonic current as the quantity of direct current. In addition, a PI control circuit is employed in the higher harmonic current control system to realize higher harmonic current control with minimum control deviation.
However, since the harmonic speed electromotive force in the dhqh-axis higher harmonic coordinate system poses a disturbance to the higher harmonic current control system, the higher harmonic current control system cannot achieve quick response simply by providing the PI control circuit in the higher harmonic current control system and, consequently, there is a problem in that the higher harmonic current cannot be reduced to a sufficient degree.
An object of the present invention is to reduce the higher harmonic current flowing to a 3-phase AC motor.
The motor control apparatus according to the present invention comprises a fundamental current control device that controls a fundamental current in a 3-phase AC motor in an orthogonal coordinate system constituted of a d-axis and a q-axis (hereafter referred to as a dq-axis coordinate system) rotating in synchronization with the rotation of the 3-phase AC motor, a higher harmonic current control device that controls a higher harmonic current in the motor in an orthogonal coordinate system constituted of a dh axis and a qh axis (hereafter referred to as a dhqh-axis coordinate system) rotating at a frequency that is an integral multiple of the frequency of the fundamental component of the current flowing to the motor, an estimating device that estimates the level of the harmonic speed electromotive force in the motor in the dhqh-axis coordinate system and a compensating device that compensates the harmonic speed electromotive force estimated by the estimating device.
In the motor control method adopted in a motor control apparatus having a fundamental current control device that controls a fundamental current in a 3-phase AC motor in an orthogonal coordinate system constituted of a d-axis and a q-axis rotating in synchronization with the rotation of the 3-phase AC motor and a higher harmonic current control device that controls a higher harmonic current in the motor in an orthogonal coordinate system constituted of a dh-axis and a qh-axis rotating at a frequency that is an integral multiple of the frequency of a fundamental component of the current flowing to the motor, a harmonic speed electromotive force in the motor in the dhqh-axis coordinate system is estimated and the estimated harmonic speed electromotive force is compensated.